1. Field of the Invention
The present invention is related to a lens unit employed for cameras and the like. More specifically, the present invention is related to a lens unit equipped with a lens and a lens barrel for holding the lens, that adjusts the position of the lens utilizing an optical path extending member provided within the lens barrel.
2. Description of the Related Art
In a lens unit having groups of fixed lenses (lenses which are not moved in the direction of the optical axis during use) at the side closest to an object, such as the zoom lens of a camera, the refractive power of the lens groups becomes great as the total length of the lens unit becomes shorter. Therefore, axial shifting and inclinations among the lens groups are reflected in focusing states, which result in deteriorations in imaging quality.
Particularly in a bending optical system equipped with an optical member that bends the optical path 90 degrees within lens groups, such as that illustrated in U.S. Pat. No. 7,471,471, lenses having greater refractive powers are used to achieve the objective of such a construction, that is, miniaturization. Therefore, axial shifting and inclinations among the lens groups are even more likely to result in deterioration in imaging quality.
In order to avoid such problems, it is necessary for each lens that constitutes the lens groups to be mounted in a state that enables a predetermined level of optical performance to be obtained, without eccentricities or axial shifting. For this reason, it is necessary for positional adjustment procedures to be performed on lenses to achieve this state, in zoom lenses and the like.
When the positional adjustment of the lenses is performed, it is common for the positions of the aforementioned fixed lenses to be adjusted while they are held in a lens barrel. In the case that the fixed lenses have a positive refractive power, a focal image which is focused by the lenses is observed with a microscope, and the positions of the lenses are adjusted based on the observation results.
In the conventional method for adjusting the positions of lenses that utilizes a microscope, a problem is recognized that it is difficult to observe the focal image with the microscope. Hereinafter, this problem will be described in detail with reference to FIG. 3 and FIG. 4.
In FIG. 3 and FIG. 4, reference numeral 1 denotes a lens barrel, reference numerals 2 and 3 denote fixed lenses, through which light 4 from an object enters, and reference numeral 5 denotes a microscope which is used to observe a focal image. As explained previously, in the case that the fixed lenses have a positive refractive power, the focal position A thereof is at a position close to the lenses 2 and 3. In the case that the observation position B of the microscope 5, which abuts the rear end of the lens barrel 1 is at the position illustrated in FIG. 3, it is not possible to observe the focal image with the microscope 5. Under these circumstances, it becomes necessary to provide the microscope 5 such that the front end thereof is positioned forward of the rear end of the lens barrel as illustrated in FIG. 4, to enable observation of the focal image. However, it is generally not possible to adopt this configuration, because the microscope 5 and the lens barrel 1 interfere with each other. Foaming the lens barrel 1 to be of a specialized construction that enables the microscope to be inserted into the lens barrel 1 may be considered. However, in this case, the cost of the lens barrel increases, and consequently results in the lens unit becoming expensive, which is a problem.
There is demand to facilitate observation using a microscope, when adjusting the positions of lenses to achieve a state that enables a predetermined level of optical performance to be obtained, by observing focal images focused by lenses held in a lens barrel with the microscope.
A method for adjusting the positions of lenses that utilizes an optical path extending member is being considered for this reason. This method for adjusting the positions of lenses is a method for adjusting the positions of lenses in a lens unit comprising a lens, through which light from an object enters, and a lens barrel for holding the lens, comprising the steps of:
observing a focal image of the lenses with a microscope; and
adjusting the positions of the lenses based on the results of observation; characterized by:
an optical path extending member being provided within the lens barrel toward the rear of the lenses, to extend the focal position of the lenses toward the rear, that is, away from the object; and
the observation of the focal image being performed in this state.
When executing a method for adjusting the positions of lenses such as that described above, it is necessary to accurately provide the optical path extending member at a predetermined relative position with respect to the lens barrel.